2. What are the health effects of solar UV radiation?

2.1 What are the benefits of solar UV radiation?

Vitamin D is produced when skin is exposed to a type of solar UV radiation (UVB). This vitamin, that many people do not produce sufficiently, is essential for maintaining healthy muscles and bones and a lack of it can result in rickets.

Vitamin D may also be important in other aspects of health, such as the prevention of autoimmune disorders and several internal tumours, and may help improve outcome from cancer. However, more data are needed to determine the actual role of vitamin D in those health aspects, and its association with exposure to UV radiation.

Exposure to sunlight may thus have widespread beneficial effects but it seems likely that these beneficial effects would also be achieved by eating foods rich in vitamin D or taking adequate levels of vitamin D supplements. More...

2.2 How can skin be damaged by solar UV radiation?

Short-term effects of skin exposure to UV radiation, particularly to UVB, include sunburn, which is most intense 24 hours later. Repeated exposure to UV radiation to obtain a deeper tan causes the epidermis to thicken, which results in the skin feeling dry.

Exposure to solar UV radiation can aggravate certain skin diseases and, when combined with some commonly used medicines and chemicals, can cause the skin to react abnormally to light. It can also affect the immune system, and this may play a role in skin cancer and some infectious diseases.

The risk of developing these cancers depends strongly on skin type. It is highest in people who sunburn easily (skin types I and II), and lowest in people with low susceptibility to sunburn (skin types V and VI). SCC is associated with continued long-term sun exposure and is more common in people who work outdoors whereas BCC is associated with intermittent exposure.

Melanoma skin cancer is much less common than non-melanoma skin cancers, but is the main cause of death from skin cancer.

The risk of developing melanoma depends on skin type. It is very low in black skinned people and highest in pale skinned individuals. People at higher risk include those with a tendency to burn rather than to tan, those who have freckles, those with fair (particularly red) hair, as well as those with a large number of moles.

Family history is an important risk factor for melanoma. For instance, the risk is twice as high in the close relatives of anyone who has had melanoma compared to people with no family history of melanoma.

Sun exposure is the main environmental risk factor for melanoma, but the pattern of exposure is also important and the risk seems higher in people who are exposed to the sun intermittently. Sunburn, particularly in childhood, may also be a significant risk factor.

The presence of multiple risk factors in an individual increases the relative risk of melanoma.

Exposure of the skin to UV radiation also results in photoageing, which is characterized by the skin becoming loose, wrinkled and with flat brown spots. Photoageing is due in part to the degradation of collagen (the major structural protein of the skin) by UV radiation. More...

2.3 How can the eyes be damaged by solar UV radiation?

The eye is a complex organ with several layers that receives visible radiation on its innermost part, the retina. The layers in front of the retina – the cornea, the lens and the vitreous humor – protect the retina from ultraviolet damage by absorbing and attenuating a significant part of the radiation.

The only short-term health effect of UV radiation on the eye is a kind of “sunburn” of the eye known as photokeratitis, a painful but temporary inflammation of the cornea that appears typically 6 – 12 hours after exposure and usually resolves within 48 hours.